1. Technical Field
The present invention relates generally to filament lamps for heating disk-shaped workpieces and, more particularly, to a filament lamp for heating a semiconductor wafer in such a way that the filament lamp and the semiconductor wafer rotate relative to each other.
2. Description of the Related Art
As is well known to those skilled in the art, filament lamps are widely used as heating sources for heat treatment such as annealing, oxidation, diffusion when forming a film such as an oxide film, a metal film or a semiconductor film on a substrate, e.g. a semiconductor wafer, or the like.
A heating apparatus using such a heating source is generally configured such that the heating source heats a workpiece when the workpiece is rotating. This technique was disclosed in Japanese Patent Application Publication No. 2010-086985 (Prior Art Document 1).
However, the conventional heating apparatus uses a linear tubular lamp, which may easily cause nonuniformity in light radiation between a central portion and a perimeter portion of a workpiece. FIG. 9 shows this nonuniformity phenomenon. When a linear tubular lamp 20 radiates light onto a workpiece W that is rotating, a light radiation rate is different between a central portion A and a perimeter portion B of the workpiece W. As a result, the central portion A of the workpiece W is heated to a high temperature, while the perimeter portion B thereof is heated to a lower temperature. As such, if the overall area of the workpiece W is not uniformly heated, it is impossible to reliably and uniformly process the workpiece. This causes a defective product.
In an effort to overcome the above problem, a heating source having a plurality of annular lamps which face a rotating workpiece was proposed in Japanese Patent Application Publication No. 1999-176389 (Prior Art Document 2). The structure of this heating source is illustrated in FIG. 10. Referring to FIG. 10, the annular lamps 30, 31, 32 and 33 are concentrically arranged. The annular lamps 30, 31, 32 and 33 are individually controlled to uniformly heat the overall area of a workpiece.
However, as shown in FIG. 11, even though the annular lamps that are concentrically arranged on the same plane radiate light onto the workpiece, because areas of the workpiece that correspond to spaces between the lamps do not pass just below the lamps, radiation is applied to these areas with less intensity than it is to those of areas of the workpiece that are disposed just below the lamps. As a result, heating temperature with respect to the radial direction of the workpiece becomes non-uniform.
Furthermore, this conventional technique requires the several annular lamps to be arranged on the same plane, thus making the electrical wiring for the lamps very complex.